The invention relates to control valves, and more particularly to fluid flow control valve assembly with independent feedback pressure.
Fluid flow control valve assemblies are commonly used for controlling the flow of fluid, such as hydraulic fluid, air, and the like, into and out of cylinders to extend and retract a ram. The control valve assemblies typically include a fluid supply passageway that supplies fluid to the cylinder and a fluid exhaust passageway that exhaust fluid from the cylinder. A multi-position valve can be provided that controls the flow of fluid through the passageways.
A known fluid flow control valve assembly for operating a single acting cylinder is disclosed in U.S. Pat. No. 4,823,550. The control valve assembly includes a manually operable rotary multi-position flow control valve that controls the flow of fluid through a fluid supply passageway and a fluid exhaust passageway formed through a valve block. A fluid bypass passageway formed in the control block includes a venturi nozzle. The fluid exhaust passageway intersects the fluid bypass passageway downstream of a venturi nozzle, such that fluid is quickly drawn out of the cylinder by fluid pumped through the venturi nozzle.
The manually operable rotary multi-position flow control valve controls the flow of fluid through the passageways in the valve block, and has three positions: a load position, a hold position, and an unload position. In the load position, fluid is pumped through the control valve into the cylinder. In the hold position, the control valve blocks all flow into and out of the cylinder. Finally, in the unload position, the control valve directs fluid through the venturi nozzle and allows fluid to flow out of the cylinder. In one embodiment, disclosed in the patent, a check valve that blocks fluid flowing out of the cylinder opens in response to fluid directed to the venturi nozzle.
It is often desirable to control a cylinder using an electrically or pneumatically operated flow control valve in cooperation with a pilot operated check valve that can hold fluid in the cylinder with the flow control valve in the reset position. A pilot operated check valve includes a pilot line, and opens in response to a feedback pressure in the pilot line. Unfortunately, the above control valve assembly does not provide a feedback pressure independent of the flow control valve position, and thus cannot be operated using an electrically or pneumatically operated flow control valve in cooperation with a pilot operated check valve that can hold fluid in the cylinder with the flow control valve in the reset position. Therefore, a need exists for a flow control valve assembly that can control a cylinder using an electrically or pneumatically operated flow control valve in cooperation with a pilot operated check valve that can hold fluid in the cylinder with the flow control valve in the reset position.